Method of making a wire plexus



Nov. 15, 1966 R. B. REID ETAL METHOD OF MAKING A WIRE PLEXUS 5Sheets-Sheet 2 Original Filed May 8, 1961 INVEN 0R5 a ea f 5. 82

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Nov. 15, 1966 R. B. REID ETAL,

METHOD OF MAKING A WIRE PLEXUS 3 Sheets-Sheet 5 Original Filed May 8,1961 INVENTOR5 Jf w erg E. gee JPmcenm United States Patent Ourinvention relates to thermal boundary construction, and particularly toan improved wire plexus for use as a substrate in thermal boundaries,such as rocket nozzle liners and the like, and to a novel method ofmaking the same. This application is a division of our copendingapplication, Serial Number 108,391, filed May 8, 1961.

In a copending application by Robert B, Reid, for Thermal BoundaryConstruction, which is assigned to the assignee of this application, athermal boundary construction is disclosed which comprises a plexus ofinterconnected metal filaments coated with a refractory material. It isthe object of the present invention to facilitate the manufacture of aplexus for this purpose, while improving the performance and increasingthe life of this type of thermal boundary.

Our invention will be described with particular reference to rocketnozzles, since the liners for such nozzles present all the problemsencountered in other thermal boundaries. However, many other uses towhich our invention can be put will be suggested to those skilled in theart as our description proceeds.

The corrosive incandescent gases to which a rocket nozzle is exposedrequire the nozzle to be made of a material both chemically inert andhighly resistant to thermal shock. These conflicting requirements can bemet successfully, in the manner described in the above-mentionedcopending application, by embedding a substrate of interconnected metalfilaments in a matrix of refractory material. In such a construction,the inert, high melting refractory material forms the gas contactingsurface, and the metal filaments serve to increase the physical strengthof the nozzle, not only because of their inherent strength, but becausethey reduce the thermal gradients through the layer nearest the hot gasstream and thereby reduce thermal shock, at the same time inhibiting thepropagation of any thermally induced cracks in the refractory materialand holding in place any fragments that might otherwise be broken off.

The extent of the advantages obtained by the construction described inthe above copending application depend in large part on the intricacy ofthe metal plexus used as the substrate, and on the amount of metal thatcan be incorporated without making the plexus unduly stiff. Theintricacy of the plexus is important, because the shorter the paththrough the refractory between a given filament and the next, the moreefiicient is the plexus, both in lowering the thermal gradient from thegas stream to the body of the rocket, and in inhibiting the propagationof cracks. The more metal that can be included, the better, since ahigh-melting metal such as tungsten best meets the requirements of anozzle material, except in the surface layer which is subject toerosion, and in the necessary heat insulation between the nozzle linerand the body of the rocket. The plexus should not be made unduly stiff,because the thermal expansion or construction of the elements of theplexus should be independent. For example, a solid annular ring of metalwould be an undesirable substrate, because it might tend to warp as aunit in a way that would fragment the refractory material.

Numerous constructions might be devised which would, in principle, meetall of the requirements of a successful plexus outlined above. However,to produce such construction in quantity, without an exhorbitantexpenditure of time and money, could present a ditficult problem. Inaccordance with our invention, the problem is solved by using a novelprocess involving simple procedures and little equipment, which resultsin a plexus of greatly improved life and performance, and one that canbe designed for maximum efficiency in the regions of greatest thermalstress.

Briefly, the novel process of our invention comprises interlinkinghelical coils of wire arranged in a parallel array, in a simple sequenceof steps, in such a way that the coils are tightly interconnected inareas of maximum thermal stress, and have protruding unlinked portionsin areas of lesser thermal stress; placing transverse strands of wireacross the protruding ends, and interlinking the protruding ends withthe transverse strands by helical coils of wire threaded through theprotruding ends. The novel plexus produced by this process is highlyintricate, and has a high concentration of metal in the areas of maximumthermal stress.

The process of our invention, and the novel product produced thereby,will best be understood by reference to the accompanying drawings,together with the following detailed description, of a preferredembodiment thereof,

FIGURE 1 is a schematic diagram illustrating the first step in theproduction of a plexus in accordance with our invention;

FIGURE 2 is a schematic diagram illustrating the second step in theproduction of a plexus in accordance with our invention;

FIGURE 3 is an elevational view of a mandrel used in the process of ourinvention;

FIGURE 4 is an end view illustrating the third step in the production ofa plexus in accordance with our invention;

FIGURE 5 is a schematic diagram illustrating the fourth and fifth stepsin the production of a plexus in accordance with our invention;

FIGURE 6 is a pictorial view, with areas enlarged, illustrating thegeneral appearance and certain detailed aspects of a plexus inaccordance with our invention; and

FIGURES 6A and 6C are enlarged, fragmentary views of a section of theplexus according to our invention;

FIGURE 6B is an enlarged, fragmentary view of the inner section of theplexus of our invention;

FIGURE 7 is a cross-sectional view, with a portion enlarged, of a rocketnozzle in accordance with our invention; and

FIGURE 7A is an enlarged, fragmentary, cross-sectional view of a sectionof the internal throat of the embedded plexus in accordance with ourinvention.

Referring now to FIGURE 1, the first step in the production of a plexusin accordance with our invention is the manufacture of a plurality ofsubassemblies made by threading an elongated helical coil of wire 1, ofa first length, into two shorter coils 2 and 3 of a second length, thefirst coil being carried through coils 2 and 3 until it protrudes on theother side as shown.

Next, as shown in FIGURE 2, two subassemblies are arranged side by sideand interconnected by threading a coil 4 of the first length throughadjacent shorter coils of the subsassemblies. The plexus 5, formed byrepeating this process and adding subassemblies, can be continued to anydesired length.

The next step in the formation of an annular plexus in accordance withour invention requires a suitable mandrel complementary in shape to thesurface comprising the'thermal boundary to be formed. FIGURE 3 shows ahyperboloidal mandrel suitable for use in making a plexus for a rocketnozzle. As shown, it comprises a lower member 6 secured to an uppermember 7 by a bolt 8 extending through a central aperture in members 6and 7. A washer 9 is placed over the end of bolt 8 and secured by asuitable means such as a nut 10 engaging threads formed on bolt 8.

Referring now to FIGURE 4, in conjunction with FIG- URES 2 and 3, theplexus is next wrapped around the mandrel and its end coils 2 and 3 arejointed by threading an additional coil 12 of the first length throughtheir turns to form a closed link comprising the central portion of theplexus, which portion is now completed and forms the strongest and mostintricate portion of the structure, since it is in the region of thenozzle throat at which the maximum stress and erosion occur.

Referring now to FIGURE 5, the mandrel is next secured in a suitablerotatable chuck 13, and transverse strands of wire 14 and 15 are woundacross the protruding ends of coils 1, 4 and 12. The winding may bestarted be securing one end of each of wires 14 and 15 to any of thecoils 1, 4 and 12 by a single turn around it, and then continued byrotating chuck 13 to take wire from a spool 16 rotatable disposed on ashaft 17 and adapted to be moved along shaft 17 in the direction of thearrows. Similarly, wire 15 is drawn from a spool 18 slidably androtatably disposed on a shaft 19.

When the winding is completed, essentially as shown for the portionoverlying element 6 of the mandrel, transverse windings 14 and 15 arecut, and may be secured at the end of any of the protruding coils 1, 4and 12 by a turn. It may be noted at this point that the only reason forusing different reference numerals to distinguish coils 1, 4 and 12 isto aid in visualizing the process by which they were assembled, since inphysical respects these coils may be identical.

After the Winding of strands 14 and 15 has been completed, thetransverse strands are secured to the longitudinal coils 1, 4 and 12 bythreading coils 20 through their turns and around the transverse strandsat each intersection. Coils 20 are each of the length of a protrudingend of one of coils 1, 4 and 12 on one side of the central portion ofthe plexus 5.

FIGURE 6 shows, in somewhat schematic and pictorial fashion, the generalappearance of a completed plexus in accordance with our invention. Asshown, the central portion of the plexus comprises a tightly interlinkedmass of wire formed by the interlinked turns of coils 1, 2, 3, 4, and12. No attempt has been made to show these interlinkings in detail, butthe general texture is indicated in the enlargement of FIGURE 63.

The lower portion 21 of the plexus has been distorted in FIGURE 6 tomore clearly illustrate its construction, and in FIGURE 6A the manner inwhich transverse strands 14 are held in place by coils 20 threadedthrough coils 1 and 4 is pictorially illustrated.

As shown in FIGURE 6A, if desired in certain areas, the entrance andexit portions of the plexus can be reinforced by longitudinal strands 22inserted through coils 1 and 20 and held between the turns of thesecoils and transverse strands 14. This permits the addition of additionalmetal in a very simple manner.

If desired, the outer rims of the entrance and exit portions can befurther reinforced by weaving transverse strands 23 and 24 in and out ofthe coils.

When completed, the plexus is removed from the mandrel by removing nutand pulling member 6 and 7 apart.

Referring now to FIGURE 7A, the completed plexus 5 is embedded in alayer of refractory material 25 to form a solid nozzle liner, as byflame spraying of the refractory material on the plexus, and thecompleted liner may then be attached to a refractory member 26, whichserves both as a heat insulator and as a means of attachingthe nozzle tothe rocket. If desired, as described in the above mentioned copendingapplication, the plexus may be coated with refractory material while inplace on form 26, and the nozzle thus formed integrally in one step. Theenlargement in FIGURE 7 shows somewhat pictoraially a cross sectionthrough the refractory material 25, illustrating the manner in which theindividual coils contribute to the distribution of metal through arelatively thick layer nearest the gas contacting surface of therefractory 25.

The Wire used to form the plexus of our invention may be of any suitablephysically strong high melting metal, such as tungsten or the like, andthe refractory material used to; coat the plexus may be any of the knownrefractories, such as graphite, hafnium carbide, boron nitride, titaniumcarbide, titanium boride, tantalum carbide, or solid solutions ofhafnium and tantalum carbide, in powdered form.

While we have described only one embodiment of our invention, in detail,many changes and variations will be apparent to those skilled in theart, and such may obviously be made without departing from the scope ofour invention.

Having thus described our invention, what we claim is:

1. The process of making a wire plexus, comprising the steps of: makinga plurality of subassemblies, each subassembly being made by threading afirst helical coil of Wire of a first length through two shorter coilsof a second length to link them together with the first coil protrudingat both ends; arranging the subassemblies side by side and linking theadjacent shorter coils of adjacent subassemblies by threading a coil ofthe first length through them; wrapping the plexus so formed around amandrel; linking the shorter coils at the ends of the plexus bythreading a coil of the first length through them; wrapping a strand ofwire around the mandrel and between the turns of the protruding ends ofthe first coils; and securing the transverse strands to the first coilsby threading a coil of Wire through each first coil.

2. The process of making a rocket nozzle liner, comprising the steps ofinterlinking the turn of a parallel array of helical wire coilsalternately of a first length and a shorter second length, the coils ofthe second length being disposed intermediate the ends of the coils ofthe first length, wrapping the plexus so formed about a hyperboloidalmandrel having regions complementary in shape to the entrance, exit andthroat portions of a rocket nozzle, securing the end coils of the plexusby interlinking their turns with a helical coil of wire, wrapping aplurality of turns of wire transversely about the protruding ends of thecoils of the first length in the entrance and exit regions, securingeach coil of the first length to the transverse turns by a helical wirecoil threaded into it and around each transverse turn at itsintersection with the coil, removing the plexus from the mandrel,coating the plexus with a layer of refractory material, and fusing therefractory layer to form a smooth gas contacting surface.

3. The process of making a wire plexus for use as a substrate in theconstruction of a thermal boundary, comprising the steps of interlinkingthe turns of a parallel array of helical wire coils alternately of afirst length and a shorter second length, the coils of the second lengthbeing disposed intermediate the ends of the coils of the first length,wrapping the plexus so formed about a hyperboloidal mandrel, securingthe end coils of the plexus by interlinking their turns with a helicalcoil of wire, wrapping a plurality of turns of wire transversely aboutthe protruding ends of the coils of the first length, and securing eachcoil of the first length to the transverse turns at their mutualintersections by threading helical coils through the turns of each coilof the first length.

4. The process of making a plexus for use as a thermal boundarysubstrate, comprising the steps of arranging a first plurality ofhelical wire coils in a nonintersecting array, placing a nonintersectingarray of transverse strands across said coils, and threading one of asecond plurality of helical wire coils through the turns of each of saidfirst coils to link the coils and the transverse strands at theirintersection.

5. The process of making a wire plexus, comprising the steps ofthreading a first helical coil through the turns of a second, threadinga third helical wire coil through the turns of the second, repeating thethreading of coils 10 the ends of the plexus by threading a helical coilthrough the turns of the coils.

References Cited by the Examiner UNITED STATES PATENTS 386,306 7/1888Emerson et al. 14092.3 X 1,306,859 6/1919 Schneider 14092.3 X 2,451,74910/1948 L. Kreisler 634 2,498,211 2/1950 J. Kreisler 14092.4

JOHN F. CAMPBELL, Primary Examiner.

P. M. COHEN, Assistant Examiner.

1. THE PROCESS OF MAKING A WIRE PLEXUS, COMPRISING THE STEPS OF: MAKINGA PLURALITY OF SUBASSEMBLIES, EACH SUBASSEMBLY BEING MADE BY THREADING AFIRST HELICAL COIL OF WIRE OF A FIRST LENGTH THROUGH TWO SHORTER COILSOF A SECOND LENGTH TO LINK THEM TOGETHER WITH THE FIRST COIL PROTRUDINGAT BOTH ENDS; ARRANGING THE SUBASSEMBLIES SIDE BY SIDE AND LINKING THEADJACENT SHORTER COILS OF ADJACENT SUBASSEMBLIES BY THREADING A COIL OFTHE FIRST LENGTH THROUGH THEM; WRAPPING THE PLEXUS SO FORMED AROUND AMANDREL; LINKING THE SHORTER COILS AT THE ENDS OF THE PLEXUS BYTHREADING A COIL OF THE FIRST LENGTH THROUGH THEM; WRAPPING A STAND OFWIRE AROUND THE MANDREL AND BETWEEN THE TURNS OF THE PROTRUDING ENDS OFTHE FIRST COILS; AND SECURING THE TRANSVERSE STRNDS TO THE FIRST COILSBY THREADING A COIL OF WIRE THROUGH EACH FIRST COIL.